This invention relates to a seal for a subsea well system. More particularly, this invention relates to a tapered wellhead seal having provisions to prevent water ingress into the well.
In subsea oil and gas well systems, a wellhead connector is installed onto the wellhead housing at the sea floor. For sealing between the wellhead connector and the wellhead housing, an annular gasket or seal is positioned between the connector and the housing. U.S. Pat. No. 4,474,381 dated Oct. 2, 1984 discloses a tubular joint with a metal seal ring positioned between internal tapered surfaces on the tubular members. This type of seal is for sealing against internal pressure within the tubular members.
Advances in offshore drilling technology have made it possible to drill in deeper water than ever before. As drilling depths increase, so does the water pressure at the sea floor. New seals had to be designed to withstand the increased external pressure when the internal pressure is lower than the external pressure. U.S. Pat. No. 5,839,765 dated Nov. 24, 1998 discloses a metal seal ring which creates a metal-to-metal seal against internal pressure within the tubular members. A pair of O-ring seals mounted to the seal rib creates a secondary seal to prevent the ingress of sea water into the joint. O-ring seals have also been used on the outer sides of the primary seal surfaces to prevent ingress of sea water.
Although the secondary O-ring seal represents an improvement over the prior art, further improvements are desired. O-ring seals are prone to deteriorate in the environment of a subsea wellhead. Replacing a seal on a gasket of a connector would be difficult and expensive. It is desirable to provide a seal which can seal against internal and external pressures without requiring the use of elastomers.
The present invention relates to an improved seal for a subsea wellhead connector. The seal of the invention includes a metal seal with a ring portion and a rib portion. The rib portion extends radially outward from the ring portion. The ring portion includes two frustoconical surfaces for mating with tapered surfaces of the wellhead connector and wellhead housing. Two conical, metal-to-metal seals are created where the ring portions of the seal engage the tapered surfaces of the wellhead connector and housing. These metal-to-metal seals are the primary seals to contain internal pressure within the wellhead.
In a preferred embodiment, two legs extend outward from the rib portion. An upward-facing foot surface at the end of the upper leg engages the wellhead connector, while a downward-facing foot surface at the end of the lower leg engages the wellhead housing. A metal-to-metal seal is created between each foot surface and the corresponding tubular member. These seals resist external pressure to prevent water ingress into the joint.